I noticed the status event method as well but didn't think to make an override for it! I also tried overriding dispatchEvent() to see if I could find any other events that trigger at any point and found none. It might just be some framework meant to get data from Twitter/Facebook that was never implemented. I did find that the statusEventHandler does trigger for "cancel" and "post" for both Twitter and Facebook so I was able to fix the problem I was having (which was an event triggered for cancel but no event was dispatched if they post so I couldn't figure out how to restart the app if they post). Not sure why your test indicated that it didn't work for twitter but it worked for me.
No way to actually tell if something was actually post though (maybe for future implementation). The farthest I could dig was an ExtentionConText object (the target of the statusEventHandler event), but theres no documentation on what functions are available through it. I'm kind of surprised the gaming SDK is not open source but does not even have documentation for native features and function within the native classes. Most of it seems to work great but its problematic that they provide almost no documentation or references to work off of despite the fact they apparently tested these things.